Device and method for severing a thread

ABSTRACT

The invention relates to a device ( 1 ) for severing a thread that comprises two blades ( 2, 3 ). An electric drive ( 4 ) enables said blades to be moved counter to the action of leaf springs ( 6, 7; 9, 10 ) and into a ready position, from which the blades can be moved back by means of the force of the leaf springs in order to execute a severing process.

The invention relates to a device for severing a thread that has twoblades, at least one of which is movable relative to the other by meansof an electric drive, and to a method for severing a thread.

A device for severing a weft thread for a weaving loom is known (GermanPatent Disclosure DE 2230099), which has two blades that are movablerelative to one another. This device is located in the vicinity of thefabric edge, in order to cut off a weft thread that is picked up by agripper and transported into the shed. To improve the cutting operation,the blades are pressed against one another by spring force. One of theblades is driven via a cam system, which in turn is driven by theweaving loom. Such a device has the disadvantage that the speed ofmotion of the blades in cutting off the thread is determined by thespeed of the drive means, whose speed is determined by the speed of theweaving loom.

A device of the type defined at the outset is also known (EuropeanPatent Disclosure EP 0284766 A1), which as its drive includes anelectric drive motor. In this known device, one problem is that therelative speed of the blades upon severing a thread is determined by theactivating and properties of the electric drive means.

The object of the invention is to create a device of the type defined atthe outset in which the speed of motion of the blades during thesevering operation is independent of the speed of the weaving loom or ofproperties of an electric drive.

This object is attained in that the at least one movable blade ismovable by the drive counter to the action of at least one springelement into a ready position from which, by means of the force of theat least one spring element, it can be moved back again for executing asevering operation.

The invention offers the advantage that the speed of motion of theblades is independent of the drive means and can thus be selected as afunction of the thread to be severed, in particular a weft thread of aweaving loom. The speed of the relative motion between the blades isdetermined essentially by the natural frequency of the means that retainthe movable blade and that move with the blade.

The application of the device according to the invention to weavinglooms leads to the advantage that the speed of severing is independentof the weaving speed of the weaving loom and independent of the responsetimes and reaction times of the electric drive means. The speed for thecutting can be set adequately high in all cases to enable satisfactorysevering of a weft thread. This is advantageous above all whenever thepower loom is operated at slow speed, and a weft thread has to besevered or cut.

According to an embodiment of the invention, it is provided that bothblades can be moved into a ready position with contrary motion by meansof electric drives and can be moved back again by means of springelements. Thus substantially higher cutting speeds can be attained thanwith one stationary blade and only one moving blade. In a furtherembodiment of the invention, it is provided that the blade or blades areeach retained by respective pairs of leaf springs, which are orientedtransversely to the direction of motion of the associated blade and aredisposed spaced apart from and parallel to one another. Since the bladesneed not execute excessively great motions, and since the leaf springsin turn can have a relatively great length, it is possible in this wayto move the blades substantially rectilinearly, without having toprovide guides for the purpose.

In an embodiment of the invention, it is provided that the blade orblades are connected to an armature which contains at least onepermanent magnet and with which an electromagnet is associated. Infurther embodiment both blades are provided with armatures in which thepermanent magnets are arranged such that like poles face each other inthe ready position and unlike poles face each other in the severingposition. In this arrangement, the armatures and thus the blades attractone another while they are in the region in which the severing operationtakes place. The cutting operation is thus improved. The armatures andhence also the blades repel one another, however, while they are in theregion of the ready position, and as a result wear to the blades movingrelative to one another is reduced.

As an embodiment of the invention, one common electromagnet is providedfor the armatures of both blades; and the permanent magnets of thearmatures are oriented in opposite directions. The common electromagnethas the effect that upon its excitation, the two armatures are movedwith their blades in opposite directions.

In a preferred embodiment, it is provided that the two units comprisinga blade, an armature, and leaf springs are designed for differentnatural frequencies. By the choice of the mass of the unit comprisingthe leaf springs, armature and blade, and the choice of the springcharacteristic curve for the leaf spring, the natural frequency can bedefined. It is advantageous if the speeds of motion, selected by meansof the natural frequency, are set so differently that the position inwhich the cutting is done differs from the position of repose when theelectromagnet is not excited. It can thus be attained that in gripperlooms, in a position of repose assumed when the electric drive means arenot excited, the device is located above the fabric, so that uponbeating up, the weft threads can pass underneath the device.Nevertheless, the weft threads can be severed at the level of the planeof the fabric. This mode of operation is made possible whenever theblade that is moving downward is faster than the blade that is movingupward. The different speed and hence a different course of motion canbe attained by providing that leaf springs of different stiffness orwith a different spring characteristic curve, and/or armatures ofdifferent mass, and/or blades of different mass are used. Each of theseprovisions contributes alone or in combination with other provisions toa change in the natural frequency.

In a preferred embodiment, for a control unit of the electric drive ordrives, a CAN bus system is provided.

The object is attained by a method in which the electric drive moves theat least one blade into a ready position counter to spring force, andfor executing a severing operation, this blade is moved back again fromthe ready position at least by means of the spring force.

In a refinement, the electric drive is activated while the associatedblade is being moved back from the ready position by means of springforce. Thus the speed and the course of motion during the severing canboth be varied. In particular, it is provided that the electric drivebrakes the associated blade during the motion back from the readyposition, particularly after the severing operation has been performed.

In a further embodiment of the invention, a signal dependent on themotion of an armature of the electric drive is formed, by means of whichthe course of motion of the associated blade is monitored. This signal,which comprises a voltage, for instance, serves as feedback forcontrolling the device of the invention.

Further characteristics and advantages of the invention will becomeapparent from the ensuing description of the exemplary embodiments shownin the drawings.

FIG. 1 shows a device according to the invention in a position ofrepose;

FIG. 2 shows the device of FIG. 1, with a few components having beenleft out to increase the clarity;

FIG. 3 is a vertical section through FIG. 2;

FIG. 4 shows the device of FIG. 1 (leaving out additional components) ina ready position;

FIG. 5 shows the device of FIG. 1 in a severing position; and

FIG. 6 is a fragmentary view in the direction of the arrow F6 of FIG. 1.

The device according to the invention shown in FIG. 1 has two blades 2and 3, movable relative to one another, and electric drive means formoving these blades 2, 3 relative to one another. The blade 2 isconnected to an armature 5, which is retained movably by means of leafsprings 6, 7. The blade 3 is connected to an armature 8, which isretained movably by means of leaf springs 9, 10. The leaf springs 6, 7and 9, 10 are oriented transversely to the direction of motion of theblades 2, 3 and are disposed parallel to and spaced apart from oneanother. Each of two leaf springs 6, 7; 9, 10 are located directly oneabove the other, so that thin leaf springs, which are advantageous withrespect to the service life, can be used. The armatures 5, 8 are eachretained on both ends by relatively long leaf springs 6, 7; 9, 10, sothat the armatures 5, 8 move essentially linearly. The ends of the leafsprings 6, 7; 9, 10 remote from the armatures 5, 8 are retained by meansof a holder 11 in which they are fastened. The leaf springs 6, 7 and 9,10 are embodied in one piece in the region of the holder 11, in thisexemplary embodiment. The holder 11 has a shaft 12, which is mounted forinstance by means of an arm 13 on a frame of a textile machine. Theshaft 12 is fastened between the arm 13 and a clamping element 14 and asa result can be disposed at an arbitrary axial or radial point. As aresult, the device according to the invention can be positioned relativeto a textile machine in such a way that a thread can be severed or cutoff. In this way, the device according to the invention can be disposedin a gripper weaving loom in the direction of the weft thread in apredetermined position relative to the fabric. In addition, holderelements 15 are secured to the holder 11; they carry an electromagnet16, cooperating with the armatures 5 and 8, and a control unit 17. Thecontrol unit 17 is connected to a control unit of the textile machinevia a cable 18. The control unit of the textile machine sends signals tothe control unit 17 for actuating the device 1 according to theinvention synchronously with the textile machine.

As can be seen from FIGS. 1 through 3, each electromagnet 16,cooperating with a respective armature 5 or 8, has twomirror-symmetrically disposed iron cores for the armatures 5 and 8; thatis, two iron cores 19 for the armature 5, and two iron cores 20 for thearmature 8. The iron cores 19, 20 are formed from plates. In theexemplary embodiment shown, a pair of coils 21 for the iron cores 19, 20is provided, so that both electromagnets 16 can be controlled by thesame pair of coils 21. The coils 21 are each disposed around a middlepart 22 of the iron cores 19, 20 in the region of the armatures 5, 8.The iron cores 19, 20 are secured to the holder elements 15 by means ofscrews. In a modified embodiment, the iron cores 19, 20 are embodied inone piece; that is, they comprise only one set of plates fastenedtogether. As shown in FIG. 1, a housing 23 of nonmagnetizable materialis disposed around the electromagnets 16.

In a modified embodiment, only one coil 21 is provided, which performsthe function of the two coils 21 that are connected in series. Insteadof two mirror-symmetrically disposed iron cores 19, 20 for the armature5 and for the armature 8, it is also possible for a single iron core tobe used, while the other is replaced by a beam that is either disposedin stationary fashion or is connected to the associated armature. Inanother modified embodiment, each electromagnet 16 that cooperates withone of the armatures 5 or 8 is controlled by its own coil.

As can be seen in FIG. 2, two permanent magnets 24, 25 are accommodatedin the armature 5 and two permanent magnets 26, 27 are accommodated inthe armature 8. These permanent magnets 24 through 27 have a rodlikeshape and have two poles. The north-south direction of the permanentmagnets 24 through 27 extend vertically to the direction of motion ofthe armatures 5 and 8. The permanent magnets 24, 25 on the one hand andthe permanent magnets 26, 27 on the other are each disposed such thatthe unlike poles border one another. Each of the permanent magnets 24through 27 has a length equivalent to approximately the magnitude of themotion of the associated armature 5 or 8 between a position of repose,with the coil not excited, and a position with the coil 21 excited. Thepermanent magnets 24, 25 are oriented with their poles oppositely to thepoles of the permanent magnets 26, 27, so that upon excitation of thecoil 21, the armatures 5, 8 are each moved in opposite directions.Because of this embodiment, it is possible for both armatures 5, 8 to beactuated with either the same coil 21 or with one coil set 21.

In FIG. 2, the blades 2, 3 are in a position of repose, in which thecoil 21 is not excited. When the coil 21 of the electric drive means 4is excited, the armatures 5, 8 move in opposite directions as far as aposition that is shown in FIG. 4. This position is called the openposition or ready position. In this position, the armatures 5, 8 andthus also the blades 2, 3 are moved counter to the force of the leafsprings 6, 7; 9, 10. The electromagnets 16 and the exciter current forthe electromagnets 16 are understood to be adapted to the strength ofthe leaf springs 6, 7; 9, 10, or else the leaf springs 6, 7; 9, 10 areadapted to the electromagnets 16 and to the exciter current. Since thelike poles of the permanent magnets 24, 26 on the one hand and thepermanent magnets 25, 27 on the other rest side by side in the readyposition, the armatures 5, 8 are pressed apart somewhat, so that theblades 2, 3 are pressed against one another with only slight force. Inthis position, a thread A to be severed or to be cut, for instance aweft thread in the case of a gripper weaving loom, is placed between theblades 2 and 3. This can be done for instance in the way described in DE2230099. Once the excitation of the coil 21 is ended, the armatures 5, 8are moved back again out of the ready position by the force of theprestressed leaf springs 6, 7; 9, 10, so that they sever the thread Alocated between the blades 2, 3, in a cutting position that is shown inFIG. 5. In this cutting position, the unlike poles of the permanentmagnets 24 through 27 face one another, so that the armatures 5, 8attract one another, which reinforces the cutting operation.

As can be seen from FIG. 5, the cutting position is located somewhatlower than the position of repose shown in FIG. 2. This is due to thefact that the blade 3 moves downward at a higher speed than the speed atwhich the blade 2 moves upward. This difference in speed is due, in theembodiment shown, to a difference in the natural frequency between theunit comprising the blade 2, armature 5 and leaf springs 6, 7 and theunit comprising the blade 3, armature 8 and leaf springs 9, 10. In theembodiment shown, the difference in the speed of motion is caused forinstance by the fact that the unit having the blade 2 is heavier andthus moves more sluggishly than the unit having the blade 3. It isunderstood also to be possible to attain a different speed of motion bymeans of varying the natural frequency of the applicable unit in someother way, in particular by varying the mass of the unit or the springstiffness of the leaf springs 6, 7; 9, 10.

In order to vary the speed of motion of the blades 2 and 3, the coil 21may also be activated. To reduce the speed of motion, it can be providedthat the excitation of the coil 21 not be interrupted, but instead thata relatively low current be made to flow through the coil. As a rule,however, the latter is unwanted, since in most cases as high a speed aspossible is advantageous for cutting. Therefore, to increase the speedof the motion, a current is passed through the coil 21 that is oppositethe current that flows through the coil 21 for putting the blades 2 and3 into the ready position shown in FIG. 4. In that case, the blades 2,3, during their motion out of the ready position, are likewisecontrolled by the electric drive means 4. However, since theacceleration and the speed reached by the leaf springs 6, 7; 9, 10 arerelatively high, in most cases activated the coil 21 with an oppositelyoriented current affects the speed of the motion during cutting onlyslightly. To limit the speed of the blades 2, 3, it is advantageous toactivated the electric drive means 4 briefly, directly after thecutting, in such a way that the blades 2, 3 are forced back into thedirection to the position shown in FIG. 4, or in other words are brakedafter the cutting.

If the device of the invention is used in a gripper weaving loom, thecoil 21 is briefly excited after the cutting—for instance as describedabove—in other to brake the blades 2, 3. After that, the unit can settlefreely until the position of repose of FIG. 2 has been resumed. Thesettling process is damped since the blades 2, 3 rest on one another andrub against one another. In a modified version, damping is accomplishedby the drive means 4. To that end, the coils 21 can be short-circuitedafter the severing operation. The motion of the permanent magnets 24through 27 generates a voltage which, with short-circuited coils 21,generates a current through the coils 21. As a result, some of theenergy of motion into the coils 21 is converted into heat. Because ofthis, moreover, the frequency of the operation can be increased further.In the position of repose of FIG. 2, a beaten-up weft thread can travelbeneath the blade 2. In gripper weaving looms, it is also important forthe instant at which the drive means are no longer activated and thesevering operation takes place to be synchronized with the weavingcycle.

The control unit 17 of the device of the invention is connected via acable 18 to a CAN bus system, so that the electric drive means, and inparticular the coil 21, can be activated via this CAN bus system. As aresult, it is possible to use the device according to the invention inany already-existing textile machine that is equipped with a CAN bussystem.

In a modified embodiment, the control unit 17 is provided with means fordetecting the course of motion of the blades 2, 3 during the motion andin particular the cutting motion. This can be done for instance bymeasuring an electrical signal that occurs in the coil 21 as a result ofthe permanent magnets 24 through 27, moving relative to the coil 21, ofthe armatures 5, 8. On the basis of this signal, the instant of cuttingcan be determined. The determination of the instant of cutting can alsobe done in some other way, such as with the aid of optical sensors, oras known from International Patent Disclosure WO 99/29946.

In gripper weaving looms, this method can for instance be employed tocompare the correct instant of cutting with the instant when the coil 21is no longer excited. The instant when the drive means 4 are no longerexcited is synchronized with the weaving cycle by setting or adjustingthe instant of the end of excitation within the weaving cycle such thatcutting is done at the correct instant within the weaving cycle. Hence acorrect setting of the instant of the end of excitation can be definedfor every device for cutting, without there being any influence by theproperties of the leaf springs, armatures or blades on thesynchronization of the instant of cutting with the weaving cycle. Such asetting can be achieved for instance by providing that the instant ofthe end of excitation of the coils 21 is set relative to the position ofthe drive shaft of the gripper weaving loom such that the armatures 5and 8, which are restrained firmly in their ready position, are releasedat that instant. The relative instant of thread cutting relatively tothe instant of the end of excitation can then be used as a feedbackvalue for setting or adjusting the instant of the end of excitationrelative to the position of the drive shaft of the gripper weaving loom.By shifting the instant of the end of excitation of the coil set 21 to agreater or lesser extent relative to a previously determined position ofthe drive shaft, the instant of cutting can be set precisely or changedby the control of the end of excitation as a function of theaforementioned, previously determined position relative to the positionof the drive shaft and thus relative to the weaving cycle.

In FIGS. 1, 3 and 6, details are also shown for how the blades 2 and 3are connected to the armatures 5 and 8. On the underside of the armature5, the leaf springs 7 are secured to the armature by means of a clampingelement 28. A T-element 30 is secured to this clamping element 28 bymeans of a screw. The blade 2 is secured to this T-element 30 byfastening means 31. The leaf springs 10 are secured to the underside ofthe armature 8 by means of a clamping element 29. By means of a screw, aT-element 32 is secured to this clamping element 29. A leaf spring 33 issecured to this T-element 32 by a fastening means 34. The blade 3 issecured to this leaf spring 33 by adhesive bonding, soldering, orwelding, or the like, for instance. By means of the fastening of theT-elements 30 and 32 relative to one another and the deformation of theleaf spring 33, the force with which the blades 2, 3 are pressed againstone another can be adjusted. By the fastening means 31 and 34, therelative height of the blades 2 and 3 with respect to one another canalso be adjusted. The blades 2 and 3 are ground in a known manner sothat they will cut optimally.

In a modified embodiment, the armatures 5 and 8 each have only onepermanent magnet, for instance the permanent magnets 25 and 26,respectively. For cutting and to avoid wear of the blades 2, 3, however,it is more advantageous to use two permanent magnets 24, 25; 26, 27each, respectively.

Different speeds for the motion of the blades 2 and 3 can also beattained by providing that in the motion toward the cutting position,the blades 2, 3 are controlled differently by the electric drive means4, by using permanent magnets of different strengths for the twoarmatures 5, 8, by activating the electromagnets 21 differently, byactivating each armature 5, 8 by a different electromagnet, or by acombination of these provisions. Moreover, an auxiliary coil may beprovided for each armature 5, 8, in order to speed up or slow down themotion of the armature 5, 8 during cutting.

In the embodiment shown, the ready position is determined essentially bythe longitudinal dimensions of the permanent magnets 24 through 27. In amodified embodiment, this position can be determined with the aid ofsensors, for instance optical sensors, that cooperate with the controlunit 17. The control unit 17 may for instance control the currentdelivered to the coil 21 such that the armatures 5, 8 assume apreviously defined ready position.

It is understood that the device of the invention is not limited to usein a gripper weaving loom. It can readily be employed in any othertextile machine in which threads must be severed, such as air jet looms,gripper shuttle looms, water jet looms, projectile looms, other types ofweaving looms, knitting machines, sewing machines, and other textilemachines. The device of the invention offers the advantage that it canbe built into any existing textile machine without problems. Aparticular advantage is that a thread can be severed at a relativelyhigh cutting speed, which can be adjusted independently of the speed ofthe textile machine and independently or at least largely independentlyof the electric drive means. Because the two blades 2, 3 move relativeto one another upon cutting, a higher cutting speed is obtained comparedto the case in which one of the blades is stationary.

The device according to the invention and the method according to theinvention are not limited to the embodiments described here as examplesand shown in the drawings. On the contrary, they may be realized invarious variants.

1. A device (1) for severing a thread (A), which has two blades (2, 3)at least one of which is movable relative to the other by means of anelectric drive (4), characterized in that the at least one movable blade(2, 3) is movable by the drive (4) counter to the action of at least onespring element (6, 7; 9, 10) into a ready position from which, by meansof the force of the at least one spring element, it can be moved backagain for executing a severing operation.
 2. The device of claim 1,characterized in that both blades (2, 3) can be moved into a readyposition with contrary motion by means of electric drives (4) and can bemoved back again by means of spring elements (6, 7; 9, 10).
 3. Thedevice of claim 1, characterized in that the blade or blades (2, 3) areeach retained by respective pairs of leaf springs (6, 7; 9, 10), whichare oriented transversely to the direction of motion of the associatedblade (2, 3) and are disposed spaced apart from and parallel to oneanother.
 4. The device of claim 1, characterized in that the blade orblades (2, 3) are connected to an armature (5, 8) which contains atleast one permanent magnet (24, 25; 26, 27) and with which anelectromagnet (19, 20, 21) is associated.
 5. The device of claim 4,characterized in that the armature (5, 8) includes two permanent magnets(24, 25; 26, 27), which contact one another with unlike poles.
 6. Thedevice of claim 4, characterized in that both blades (2, 3) are providedwith armatures (5, 8), whose permanent magnets (24, 25; 26, 27) aredisposed such that they face one another with like poles in the readyposition and with unlike poles in the severing position.
 7. The deviceof claim 1, characterized in that the length of the permanent magnets(24, 25; 26, 27) of the armatures (5, 8) in the direction of motion ofthe blades (2, 3) approximately equals to the magnitude of the relativemotion between the blades.
 8. The device of claim 1, characterized inthat one common electromagnet (19, 20, 21) is provided for the armatures(5, 8) of both blades (2, 3); and that the permanent magnets (24, 25;26, 27) of the two armatures (5, 8) are oriented in opposite directions.9. The device of claim 1, characterized in that the two units comprisinga blade (2, 3), an armature (5, 8), and leaf springs (6, 7; 9, 10) aredesigned for different natural frequencies.
 10. The device of claim 1,characterized in that for a control unit (17) of the electric drive ordrives (4), a CAN bus system is provided.
 11. A method for severing athread (A) by means of two blades (2, 3), at least one of which is movedrelative to the other by means of an electric drive (4), characterizedin that the electric drive (4) moves the at least one blade (2, 3) intoa ready position counter to spring force; and that this blade (2, 3),for executing a severing operation, is moved back again from the readyposition at least by means of the spring force.
 12. The method of claim11, characterized in that the electric drive (4) is activated while theassociated blade (2, 3) is being moved back from the ready position bymeans of spring force.
 13. The method of claim 11, characterized in thatthe electric drive (4) brakes the associated blade (2, 3) during themotion back from the ready position, particularly after the severingoperation has been performed.
 14. The method of claim 11, characterizedin that a signal dependent on the motion of an armature (5, 8) of theelectric drive (4) is formed, by means of which the course of motion ofthe associated blade (2, 3) is monitored.